1) Aperture 2) Having a mouth 3) Pore 4) Stoma 1) Hydathode 2) Lenticel 3) Stoma 
• (n.) A stoma.
any of the microscopic openings or pores in the epidermis of leaves and young stems. Stomates are generally more numerous on the underside of leaves. ... [10 related articles]
a small pore or opening on the surface of a leaf through which gaseous exchange takes place, i.e. the diffusion of carbon dioxide, oxygen and water vapor
a small pore or opening on the surface of a leaf through which gaseous exchange takes place, i.e. the diffusion of carbon dioxide, oxygen and water vapor
Sto'mate noun (Botany) A stoma. 
pore noun a minute epidermal pore in a leaf or stem through which gases and water vapor can pass
stoma (def. 1).